Field of the Invention
The present patent application relates to an optical keypad comprising at least one transparent panel comprising a plurality of apertures surrounded by closed areas, which optical keypad comprises a plurality of light-emitting diodes (LEDs) emitting modulated light and at least one receiving photo diode placed in relation to the apertures, which light from the transmitting LEDs is transmitted through the transparent panel and which light is reflected by scattering from a tool or fingertip employing a keystroke in relation to one of the apertures in the transparent panel, which reflected modulated light is transmitted back through the transparent panel and back to the receiving photo diode for demodulation.
Description of Related Art
International Patent Application Publication WO 2013/156353A1, filed on 10 Apr. 2013, having priority date on 18 Apr. 2012, entitled “Keypad assembly and method to access a car” and corresponding U.S Patent Application Publication US 2015/0084739 relate to a key-less access system for cars based on a simple detection of visible light though the windscreen. The publications WO 2013/156353A1 and US 2015/0084739 disclose an amplitude modulation of the transmitted light and amplitude demodulation of received signals.
U.S. Pat. No. 4,254,333 disclose an optoelectronic circuit element for effecting a manually controlled output signal comprising at least one radiation-emitting element, a radiation-propagating unit and at least one radiation-sensitive element, the radiation-propagating unit being a solid body which is transparent to the radiation in question and which has an interface which is exposed to radiation from the radiation-propagating unit, an identifiable change in the state of the radiation-sensitive element is affected by changes in the conditions for total internal reflection of the radiation at the interface arising from contact of an actuating body, say a finger, with said interface.